Fix Alt-modified keys on some European MS-Windows keyboards

* src/w32fns.c (deliver_wm_chars): If the reported character is
ASCII, AND Meta modifier is a candidate, behave as if Meta is
present, i.e. fall back to the legacy code.  (Bug#23251)

1 files changed, 37 insertions, 1 deletions

diff --git a/src/w32fns.c b/src/w32fns.c
index b9002bae770..c57b5a188b2 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -3154,9 +3154,45 @@ deliver_wm_chars (int do_translate, HWND hwnd, UINT msg, UINT wParam,
               SHORT r = VkKeyScanW (*b), bitmap = 0x1FF;
 
               FPRINTF_WM_CHARS((stderr, "VkKeyScanW %#06x %#04x\n", (int)r,
-                               wParam));
+                                wParam));
               if ((r & 0xFF) == wParam)
                 bitmap = r>>8; /* *b is reachable via simple interface */
+              else
+                {
+                  /* VkKeyScanW() (essentially) returns the FIRST key with
+                     the specified character; so here the pressed key is the
+                     SECONDARY key producing the character.
+
+                     Essentially, we have no information about the "role" of
+                     modifiers on this key: which contribute into the
+                     produced character (so "are consumed"), and which are
+                     "extra" (must attache to bindable events).
+
+                     The default above would consume ALL modifiers, so the
+                     character is reported "as is".  However, on many layouts
+                     the ordering of the keys (in the layout table) is not
+                     thought out well, so the "secondary" keys are often those
+                     which the users would prefer to use with Alt-CHAR.
+                     (Moreover - with e.g. Czech-QWERTY - the ASCII
+                     punctuation is accessible from two equally [nu]preferable
+                     AltGr-keys.)
+
+                     SO:   Heuristic: if the reported char is ASCII, AND Meta
+                     modifier is a candidate, behave as if Meta is present
+                     (fallback to the legacy branch; bug#23251).
+
+                     (This would break layouts
+                     - delivering ASCII characters
+                     - on SECONDARY keys
+                     - with not Shift/AltGr-like modifier combinations.
+                     All 3 conditions together must be pretty exotic
+                     cases - and a workaround exists: use "primary" keys!) */
+                  if (*b < 0x80
+                      && (wmsg.dwModifiers
+                          & (alt_modifier | meta_modifier
+                             | super_modifier | hyper_modifier)))
+                    return 0;
+                }
               if (*type_CtrlAlt == 'a') /* Simple Alt seen */
                 {
                   if ((bitmap & ~1) == 0) /* 1: KBDSHIFT */